This invention relates to a noise exposure measuring device and more particularly to means for reading-out of such device a measure of noise exposure.
The measurement of environmental noise level has been a matter of great importance now that it is understood that persons exposed to moderately high environmental noise levels over an extended period of time or to very high environmental noise levels for relatively short periods of time may experience a temporary degradation in their current efficiency of operation or even long term degradation of their health. Light, small cumulative noise exposure meters have been developed which are readily portable and can be worn on a person's clothing. These noise exposure meters integrate noise level with respect to time and provide an indication of the cumulative noise to which the subject has been exposed. Specifically, a person, usually an industrial worker, habitually exposed to what could be dangerously high noise levels, wears such a noise exposure meter on his person with a noise input microphone connected thereto by an electrical cable and the microphone itself worn in the vicinity of one of the subject's ears. Then, as the subject goes about his normal work the noise exposure meter integrates the environmental noise level with respect to time. At the completion of the work day the difference in noise exposure meter reading from the beginning of the work day to the end of the work day is considered. A difference exceeding a predetermined threshold value indicates that the cumulative noise level to which the subject has been exposed was excessive and that corrective action to attenuate the noise effects upon the subject should be initiated.
Originally these noise exposure meters were self-contained in that the cumulative noise level was continuously displayed on the face of the instrument. This proved to be unsatisfactory since the subject spent unwarranted attention examining the reading from time to time. There have also been reported cases of sabotage of the meter either to raise or lower the reading thereof within reasonable limits wherein the sabotage would not be readily noticeable by a supervisor. Subsequent models of the noise level meter concealed the indication or, even more acceptably, required a base station into which the portable unit was attached for reading out the noise level indication through an electrical connector.